Solving Charles Darwin's "Abominable Mystery"

Scientists are using chemical fossils to hunt down
one of our planet's most vexing missing links -- the first-ever
flowering plant.

April
17, 2001 -- Daffodils, tulips, roses and other flowers are
so much a part of our daily lives that we take them for granted.
Yet, how and when flowering
plants appeared on Earth remains a mystery, a question that
has gone unanswered by evolutionary scientists for more than
a century.

According to the fossil
record, mosses were the first plants to emerge on land, some
425 million years ago, followed by ferns, firs, ginkgoes, conifers
and several other varieties. Then, it seems, about 130 million
years ago flowering plants abruptly appeared out of nowhere.

Above: A fossilized flower (left) and a modern flower
(right). New evidence suggests such plants may have evolved earlier
than previously thought. Credit: Hanman's Fossils

Where did they come from, and how could they have evolved
so suddenly without any transitional fossils linking them to
other ancient plant species?

"An abominable mystery" is how nineteenth-century
naturalist Charles Darwin referred to the origin of flowering
plants, and the puzzle remains as controversial today as ever.

Now a team of Stanford geochemists has entered the debate
with evidence that flowering plants may have evolved 250 million
years ago - long before the first pollen grain appeared in the
fossil record.

"Our research indicates that the ancestors of flowering
plants may have originated during the Permian period, between
290 and 245 million years ago," says J. Michael Moldowan,
research professor of Geological and Environmental Sciences at
Stanford.

"We based our findings on an organic compound called
oleanane, which we found in the fossil record," he adds.

"This
is important and exciting work," says Bruce Runnegar, professor
of paleontology at UCLA and a member of NASA's Astrobiology Institute.
"Although this is not the first time such a claim has been
made, previous work used details of plant anatomy rather than
the biomarker molecule [oleanane]."

Left: The Chemical Structure of Oleanane. Moldowan
and his colleagues have detected Oleanane in oily rock deposits
that are hundreds of millions of years old. Credit: IUPAC

Oleanane is produced by many common flowering plants as a
defense against insects, fungi and various microbial invaders.
But the chemical is absent in other seed plants, such as pines
and ginkgoes.

Moldowan and his colleagues studied Permian-era sediments
that harbored the remains of extinct seed plants called gigantopterids.
The same sediments contained molecules of oleanane.

It would seem that gigantopterids, like many present-day flowers,
produced oleanane -- an indication that they were among the earliest
relatives of flowering plants, concludes biologist David W. Taylor
of Indiana University Southeast, a co-author of Moldowan's study.

"This
discovery is even more significant because we recently found
gigantopterid fossils in China with leaves and stems that are
quite similar to modern flowering plants," Taylor notes
- further evidence that flowering plants and gigantopterids evolved
together, roughly 250 million years ago.

Right: Archaefructus liaoningensis. The leaf-like
structures on the stem of this 140 million year old fossil are
pods containing the seeds, a characteristic unique to flowering
plants. Credit: University of Florida.

Moldowan and his colleagues note that "chemical fossils"
such as oleanane can be an important tool for studying the history
of life on Earth.

Runnegar agrees. "I would imagine that the jury will
remain out on [the origin of flowers] for some time, but this
research does open up a new approach to solving this difficult
problem." The study should also encourage astrobiologists
to seek out similar biomarkers for other significant evolutionary
events, he added.

Perhaps one day chemical fossils will help unravel Darwin's
abominable mystery once and for all.

Moldowan and his collaborators, research associate Jeremy
Dahl and graduate student David A. Zinniker, presented their
findings at the annual meeting of the American Chemical Society
(ACS) in San Diego on April 2, during a symposium titled, "Biogeochemistry
of Terrestrial Organic Matter."

Darwin's 'Abominable Mystery'
is closer to a solution
-- A Cornell botany professor says that, with the discovery of
the world's oldest flowering-plant fossil, scientists from China
and the University of Florida have made a giant leap toward solving
Charles Darwin's "Abominable Mystery," the plant world's
missing link.

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